The present invention relates to Q multiplier circuits employing regenerative feedback for signal amplification and filtering.
Referring now to FIG. 1 a typical prior art Q multiplier circuit 15 is shown as including a forward signal path 6 and a feedback signal path 8. The forward signal path 6 connects the input terminal 12 to the output terminal 14 and includes a variable gain amplifier 16 and a bandpass filter 18, as well as a signal combiner 20 adjacent to input terminal 12 and a signal splitter 22 adjacent to the output terminal 14. The feedback signal path 8 connects the signal splitter 22 to the signal combiner 20 and includes the phase shifter 24. The feedback signal path 8 is intended to provide positive feedback or reinforcement of the signals applied to the input 12 as part of the output of the amplifier 16 is directed by the signal splitter 22 through the phase shifter 24 to the signal combiner 20 where it is added to the input signal applied at the terminal 12. The band pass filter selects the operative frequency for the circuit 15 while the amplifier 16 provides gain corresponding to a predetermined amount of amplification and selectivity. Unfortunately, prior Q multiplier circuits have required manual gain adjustment and manual phase adjustment to insure maximum amplification and selectivity while avoiding oscillation and to insure that positive feedback is maintained into the forward signal path.
It is therefore an object of the present invention to provide a feedback stabilized Q multiplier circuit which is automatically regulated with respect to gain and phase in order to avoid problems with oscillation and to maintain positive feedback.
It is another object of the present invention to provide a feedback stabilized Q multiplier circuit which provides a controllable level of selectivity or Q (quality factor) regardless of the level of the input signal to the circuit.
It is a further object of the present invention to provide a Q multiplier circuit which is adapted for operating as a radio receiver preselector or a radio transmitter postselector having selectivity controllable in accordance with signal conditions.
It is yet another object of the present invention to provide a Q multiplier circuit which is adapted for use in suppressing spurious signals ordinarily generated by typical phase lock loop synthesizers.